Brushless variable speed drive for a. c. synchronous motor

ABSTRACT

A motor speed control circuit is provided for varying the speed of a motor in response to a change in an ambient parameter. An A.C. hysteresis motor is driven from a D. C. supply by a multivibrator. The multivibrator is driven in synchronism with a unijunction relaxation oscillator which oscillates at a variable frequency determined by changes in said ambient parameter. A resistive sensor means is provided in circuit with the relaxation oscillator for detecting changes in the ambient parameter. The resistance of the sensor varies logarithmically with changes in the ambient parameter. The unijunction oscillator means is provided with means to compensate for the logarithmic change in the sensor, to thereby provide an oscillator frequency which varies linearly with said ambient parameter. Since the speed of the motor is controlled by the frequency of the oscillator, the motor speed is also a linear function of the change in the ambient parameter.

Apr. 2, 1974 BRUSHLESS VARIABLE SPEED DRIVE FOR A. C. SYNCHRONOUS MOTOR[75] Inventor: John Joseph Allard, Mishicot, Wis.

[7 3] Assignee: AMF Incorporated, White Plains,

[22] Filed: Apr. 10, 1973 [211 App]. No.: 349,689

[52] US. Cl 318/138, 318/171, 318/333, 307/252 F, 331/65, 331/111,318/341 [51] Int. Cl. 02k 29/02 [58] Field of Search 318/171, 227, 230,231, 318/254, 138, 333, 334, 335, 329, 331, 345, 341; 328/145; 307/252F, 301, 293; 331/65, 66, 111

[56] References Cited UNITED STATES PATENTS 3,098,958 7/1963 Katz318/171 3,473,069 10/1969 Herbert..... 318/138 3,489,968 l/1970 Katz318/138 2,898,533 8/1959 Beckett..... 318/341 2,995,690 8/1961 Lemon318/341 3,250,066 5/1966 Engelhardt 318/329 3,613,391 10/1971 Hatter318/345 Primary Examiner-Hemard A. Gilheany Assistant Examiner--ThomasLanger Attorney, Agent, or Firm-George W. Price; John H.

Gallagher [57] ABSTRACT A motor speed control circuit is provided forvarying the speed of a motor in response to a change in an ambientparameter. An A.C. hysteresis motor is driven from a D. C. supply by amultivibrator. The multivibrator is driven in synchronism with aunijunction relaxation oscillator which oscillates at a variablefrequency determined by changes in said ambient parameter. A resistivesensor means is provided in circuit with the relaxation oscillator fordetecting changes in the ambient parameter. The resistance of the sensorvaries logarithmically with changes in the ambient parameter. Theunijunction oscillator means is provided with means to compensate forthe logarithmic change in the sensor, to thereby provide an oscillatorfrequency which varies linearly with said ambient parameter. Since thespeed of the motor is controlled by the frequency of the oscillator, themotor speed is also a linear function of the change in the ambientparameter.

23 Claims, 1 Drawing Figure VSM VSD

PATENTEDAVPR 2 I91 mmo N10 mam mI 1 I BRUSHLESS VARIABLE SPEED DRIVE FORA.C. SYNCHRONOUS MOTOR This invention relates to a transducer forcontrolling the speed of an A. C. hysteresis motor as a linear functionof a change in an ambient parameter. More specifically this inventionrelates to a motor speed control circuit having a resistance meanstherein which varies logarithmically with the change in said ambientparameter and means for operating on said logarithmic change to providea linear change in the motor speed as a function of said parameter.

Various timing devices are known for controlling the cycles of variousphysical or chemical processes. These timing devices generally includetiming motors, of the synchronous type which are driven at predeterminedsubstantially constant speeds. However, these predetermined speeds oftenbecome unacceptable and need modification as the ambient conditions ofthe processes change. Accordingly, it is often necessary to change thespeed of the timing motors as a function of the changes of the ambientconditions.

It is preferred to be able to change the speed of the timing motor as alinear function of the change in the ambient condition. This is easilydone if a linear resistance sensor is available. In this situation astandard oscillator can be employed whose frequency varies as a functionof an RCcircuit containing the linear resistance sensor. The oscillatorcan thereby drive the timing motor at a speed which varies linearly withthe change in the sensor resistance.

However, it is quite often the case that the sensor resistance does notvary linearly with a change in the parameter sensed. The resistance ofthe sensor in many cases varies logarithmically with a change in theambient parameters. Therefore, in this situation a standard type ofoscillator can not be used to provide a speed change which varies as alinear function of a change in an ambient parameter.

Accordingly, it is an object of the present invention to provide a speedcontrol circuit for a synchronous motor which varies the speed of saidmotor as a' linear function of a sensed change in an'ambient parameter.

it is another object of the present invention to'provide means for.varying the speed of asynchronous motor as a linear f unction of-achange in an ambient parameter in response to a logarithmic resistancechange in a sensor means for detecting said change in said ambientparameter.

It is a furtherobject of the present invention to provide a transducermeans for varying the cycle of a process or apparatus in response to achange in ambient conditions duringsaid cycle. I The objects of thepresent "invention are fulfilled by providing an oscillator for drivingan A.C. synchronous motor at aspeed determined by the frequency of saidoscillator. The frequency'of the oscillator is controlled by a changein'an'ambient parameter such as pressure, temperature, or humidity by asensor, the resistance of which varies as a nonlinear function of theambient parameter. The-frequency 'of the oscillator of thepresentinvention is also controlled by an additional exponential function whichismatched with the nonlinear function to provide a linear change infrequency of the oscillator with a change in the ambient paramter. Thusthe speed'of the synchronous timer motor can be controlled as a linearfunction of a change in the ambient parameter detected.' I

The objects of the present invention and the attendant advantagesthereof will become more fully apparent with reference to the followingdescription of the drawing. 7

Referring to the drawing there is illustrated a variable speed drivecircuit generally indicated VSD for a variable speed A.C. hysteresismotor VSM, which is adapted to drive a load at a predetermined speed.The load may be a timer for controlling the cycle of a process. Thefunction of control circuit VSD is to vary the speed of motor VSM as alinear function of changes in ambient relative humidity sensed byhumidity sensor HS.

A bias voltage is provided for variable speed drive VSD through A.C.supply lines AC1, AC2, and transformer Tl. Transformer T1 is notessential to this circuit but it provides a voltage reduction so tahttransistors Q3 and O4 to be described more fullyhereinafter can be lowvoltage common transistors and center tapping can be accomplishedwithout power resistors.

Diodes CR1, CR2, CR3, CR4, and filter capacitor C4 are provided forchanging A. C. to D. C. so that motor VSM is driven by a D. C. voltage.Diodes CR1 and CR2 are connected to the center tapped secondary oftransformer T1.

Diodes CR3 and CR4provide A. C. isolation for humidity sensor resistorl-lSbecause many such sensors cannot be subjected to D. C. currentswithout calibration damage.

Motor VSM is provided with a bifilar wound coil Bl having two parallelbranches each consisting of one half the turns of coil Bl for drivingmotor VSM. D. C. power is supplied to coil B1 from line DC1. Theparallel branches of coil B1 are connected in circuit with thecollectors of transistors 03 and Q4, respectively.

Transistors Q3 and 04 are connected for alternate conduction in aconventional bistable multivibrator configuration wherein the collectorof transistor O3 is coupled to the base of transistor 04 through.resistor R5 and the collector of transistor O4 is coupled to the base oftransistor Q3 through resistor R4. The emitters of transistors Q3 and Q4are coupled to a common emitter junction at line DC2. Because of thecoil inductance of B1 in the collector circuits of transistors 03 andQ4, the multivibrator will free run as an -RL multivibrator to drivemotor VSM. The multivibrator can be triggered by momentarily connectingboth bases of transistors Q3 and O4 to their emitters through diodesCR7, CR8 and buffer amplifier transistor Q2. This is done in response toa trigger pulse from unijunction transistor Q1 which periodically turnstransistor Q2 on in a manner to be described hereinafter.

The multivibrator circuit will free run as a function of the backEMF ofthe transformer action of the motor coil B1. This transformer actiononly permits a gradual build-up of motor coil current compared to theapparent impedance of the coil itself.

The transformer action of the coil B1 acts as a memory for themultivibrator to enable the multivibrator to recall-which of thetransistors Q3 and 04 was on and which transistor was off. As motordrive current flows through one branch of the coil'Bl it acts as atransformer primary and the other branch as a transformersecondary. Thesecondary furnishes an exponential base drive current to the ontransistor. During the latter part of the exponential current drivepulse, the falling value of di/dt causes the on transistor to come outof saturation and start towards cut-off. The collector current of the ontransistor changes at a slower pace due to the motor inductance. Themotor current is then diverted from the on transistor collector to theoff transistor base, thus turning it on. This transistor is regenerativeand ends with the formerly on transistor cut off and the off transistorsaturated.

The multivibrator including transistors Q3 and Q4 can be drivensynchronously by pulses furnished through transistor Q2 by a unijunctiontransistor oscillator Q1 the cathode of which is connected to the baseof transistor Q2. The pulses are supplied by the unijunction at a ratewhich varies linearly with the changes in the ambient humidity sensed byhumidity sensor HS.

In order to change the speed of motor VSM linearly with a change inhumidity sensed by humidity sensor HS the present invention makes use ofa curve or function matching technique, whereby more than one parametercontrols the frequency of unijunction transistor oscillator Q1.

A programmable unijunction transistor Q1 is provided which will fire andturn on transistor Q2 when the anode voltage A is larger than the gatevoltage G. The gate voltage G is determined by the voltage acrosscapacitor C1 connected between a current limiting resistor R9 of gate Gand line DC2. The voltage across capacitor C1 is determined from OhmsLaw as a function of the sensor resistance HS and RR, RP, and RPP. Theresistance of sensor HS varies logarithmically with a change in ambientrelative humidity but by virtue of the resistance network the voltagecoupled to the gate of O1 is changed to a substantially exponentialfunction. Therefore, the voltage across capacitor C1 varies nonlinearlywith a change in the ambient relative humidity, as determined by thesetwo nonlinear parameters.

An RC time-constant circuit including resistors R1, R8, and capacitor C2provides the anode of unijunction transistor Q1 with a voltage thatvaries exponentially with time. Capacitor C2 is connected between anodeA and line DC2 and resistors R1, R8 are connected in series between lineDC] and anode A. R8 comprises an adjustable potentiometer forselectively varying the time constant of the RC circuit.

The frequency'of oscillator Q1 is determined by the relative voltages atthe gate G and the anode A thereof. Since the voltage of the gate Gdetermines the firing voltage of the anode, then the frequency of theoscillator varies exponentially with the voltage of the gate. Thus, ifthe voltage at the gate is made an exponential function of the ambientrelative humidity, the frequency of oscillator Q1 can be made to varylinearly with a change inthe ambient relative humidity. This isaccomplished by the proper selection of resistors RR, RP, RPP, R1, R8,and capacitor C2.

to thereby drive motor VSM. The alternate conduction of transistors 03,O4 is synchronized with the firing of unijunction transistor Q1.Therefore, the motor VSM is driven at a speed determined by thefrequency of uni- 5 junction oscillator 01. Since the frequency ofoscillator In operation unijunction transistor Q1 fires and gen erates apulse on the base of transistor O2 to turn transistor Q2 on at afrequency which varies linearly as a function of a change in relativehumidity sensed by resistor HS. When transistor Q2 turns on itmomentarily connects both bases of transistors Q3 and Q4 through diodesCR7, CR8 to theemitters thereof,.which drives the multivibrator intooperation. The multivibrator operates alternately energize the coilbranches of coil Bl Q1 varies as a linear function of the change inrelative humidity sensed, the speed of motor VSM willalso vary as alinear function of the relative humidity.

Those skilled in the art will realize that the curve or functionmatching technique could be extended to yield a variable speed motorwhich varies as a nonlinear function of an input parameter which iseither linear or nonlinear. This is true because the use of aprogramable unijunction transistor permits the matching of up to fiveindependent functions by proper selection of components. These fivefunctions are the input sensor selected, the output speed desired, theRC time constant, the exponential variation of this RC time constantwith voltage at the PUT gate and the linear or nonlinear resistancevoltage divider.

What is claimed is:

l. A transducer for driving a variable speed motor at speeds which varyas a linear function of an ambient parameter comprising:

a. means for sensing said ambient parameter and generating a signalwhich varies logarithmically with said ambient parameter;

b. oscillator means coupled to said sensing means and to circuit meansfor generating a signal which varies exponentially with respect to time;

c. means for controlling the frequency of said oscillator means as acombined function of said logarithmic and exponential signals to therebyvary said frequency linearly with said ambient parameter; and

d. synchronous motor means coupled to said oscillator means, saidsynchronous motor being driven at a speed determined by the frequency ofsaid oscillator means.

2. The transducer of claim 1 wherein said ambient parameter sensed isrelative humidity.

3. The transducer of claim 1 wherein there is further provided bistablemultivibrator means for driving said synchronous motor, said bistablemultivibrator being coupled to said oscillator means to drive saidsynchronous motor in synchronism with the frequency of said oscillatormeans.

4. The transducer of claim 1 wherein there is further providedsemiconductor switch means for gating the output of said oscillatormeans to said bistable multivibrator.

5. A transducer for driving a variable speed motor at speeds which varyas a function of an ambient parameter comprising:

a. synchronous motor means;

b. bistable multivibrator means for driving said synchronous motormeans;

c. oscillator means for driving said bistable multivibrator means insynchronism with the frequency of said oscillator means, said oscillatormeans including semiconductor means having a gate electrode, an anode,and a cathode, said semi-conductor means being rendered conductive togenerate a pulse through said cathode to said multivibrator means at afrequency determined by the relative voltage at said gate electrode andsaid anode;

d. means for supplying a voltage to said anode which variesexponentially with time; and

e. means coupled to the gate electrode of said oscillator for sensingsaid ambient parameter and generating a voltage at said gate whichvaries as a function of said ambient parameter; whereby the combinedfunctions of the voltages applied to said gate and anode of saidoscillator means constrain the frequency of said oscillator means tovary as a function of said ambient parameter.

6. The transducer of claim 5 wherein said semiconductor means is aprogrammable unijunction transistor.

7. The transducer of claim 5 wherein semiconductor gate means areprovided for coupling said oscillator means to said bistablemultivibrator.

8. The transducer of claim 5 wherein said means for sensing said ambientparameter comprises resistive means, the resistance of which varieslogarithmically with the ambient parameter.

9. The transducer of claim 8 wherein said resistive means is biased withA. C. power and said oscillator means is biased with D. C. power andmeans are provided for isolating the A. C. power of said resistive meansand the DC. power of said oscillator means.

10. The transducer of claim 5 wherein said ambient paramter sensed isrelative humidity.

11. A transducer for varying the frequency of an oscillator as a linearfunction of an ambient parameter comprising:

a. means for sensing said ambient parameter and generating a signalwhich varies logarithmically with said ambient parameter;

b. oscillator means coupled to said sensing means and to circuit meansfor generating a signal which varies exponentially with respect to time;

c. means for controlling the frequency of said oscillator means as acombined function of said logarithmic and exponential signals to therebyvary said frequency linearly with said ambient parameter.

12. The transducer of claim 11 wherein said ambient parameter sensed isrelative humidity.

. 13. The transducer of claim 11 wherein there is further providedbistable multivibrator means for driving a synchronous motor, saidbistable multivibrator being coupled to said oscillator means to drivesaid synchronous motor in synchronism with the frequency of saidoscillator means.

14..The transducer of claim 11 wherein there is further providedsemiconductor switch means for gating the output of said oscillatormeans to said bistable multivibrator.

15. A transducer for varying the frequency of an oscillator as afunction of an ambient parameter comprismg:

a. oscillator means including a semiconductor means having a gateelectrode, an anode, and a cathode, said semiconductor means beingrendered conductive to generate output pulses at said cathode at afrequency determined by the relative voltages at said gate electrode andsaid anode;

17. The transducer of claim 15 wherein semiconductor gate means areprovided for coupling said oscillator means to said bistablemultivibrator.

18. The transducer of claim 15 wherein said means for sensing saidambient parameter comprises resistive means, the resistance of whichvaries logarithmically with the ambient parameter.

19. The transducer of claim 18 wherein said resistive means is biasedwith the A. C. power and said oscillator means is biased with D. C.power and means are provided for isolating the A. C. power of saidresistive means and the D. C. power of said oscillator means.

20. The transducer of claim 15 wherein said ambient parameter sensed isrelative humidity.

21. The transducer of claim 5 wherein the voltage at the gate of saidsemiconductor means varies exponentially with said ambient parameter andthe frequency of said oscillator means varies linearly with said ambientparameter.

22. The transducer of claim 15 wherein the voltage atthe gate of saidsemiconductor means varies exponentially with said ambient parameter andthe frequency of said oscillator means varies linearly with said ambientparameter. A

23. A tranducer for driving a motor at speeds which vary as a linearfunction of an ambient parameter comprising:

a. means for sensing said ambient parameter and generating a firstsignal which varies as a first nonlinear function with changes in saidambient parameter;

b. oscillator means for producing an oscillating signal;

c. circuit means coupled to said oscillator for producing a secondsignal which varies as a second and different nonlinear function withrespect to time;

d. means coupling said sensing means to said oscillator means forchanging said second signal to a third nonlinear signal;

e. said second and third signals controlling said oscillator to vary theoscillator frequency as a linear function of change in said ambientparameter;

. f. a synchronous motor; and

g. means for coupling said oscillator signal to said motor forcontrolling the speed of said motor as a linear function of change insaid ambient parameter.

1. A transducer for driving a variable speed motor at speeds which varyas a linear function of an ambient parameter comprising: a. means forsensing said ambient parameter and generating a signal which varieslogarithmically with said ambient parameter; b. oscillator means coupledto said sensing means and to circuit means for generating a signal whichvaries exponentially with respect to time; c. means for controlling thefrequency of said oscillator means as a combined function of saidlogarithmic and exponential signals to thereby vary said frequencylinearly with said ambient parameter; and d. synchronous motor meanscoupled to said oscillator means, said synchronous motor being driven ata speed determined by the frequency of said oscillator means.
 2. Thetransducer of claim 1 wherein said ambient parameter sensed is relativehumidity.
 3. The transducer of claim 1 wherein there is further providedbistable multivibrator means for driving said synchronous motor, saidbistable multivibrator being coupled to said oscillator means to drivesaid synchronous motor in synchronism with the frequency of saidoscillator means.
 4. The transducer of claim 1 wherein there is furtherprovided semiconductor switch means for gating the output of saidoscillator means to said bistable multivibrator.
 5. A transducer fordriving a variable speed motor at speeds which vary as a function of anambient parameter comprising: a. synchronous motor means; b. bistablemultivibrator means for driving said synchronous motor means; c.oscillator means for driving said bistable multivibrator means insynchronism with the frequency of said oscillator means, said oscillatormeans including semiconductor means having a gate electrode, an anode,and a cathode, said semi-conductor means being rendered conductive togenerate a pulse through said cathode to said multivibrator means at afrequency determined by the relative voltage at said gate electrode andsaid anode; d. means for supplying a voltage to said anode which variesexponentially with time; and e. means coupled to the gate electrode ofsaid oscillator for sensing said ambient parameter and generating avoltage at said gate which varies as a function of said ambientparameter; whereby the combined functions of the voltages applied tosaid gate and anode of said oscillator means constrain the frequency ofsaid oscillator means to vary as a function of said ambient parameter.6. The transducer of claim 5 wherein said semiconductor means is aprogrammable unijunction transistor.
 7. The transducer of claim 5wherein semiconductor gate means are provided for coupling saidoscillator means to said bistable multivibrator.
 8. The transducer ofclaim 5 wherein said means for sensing said ambient parameter comprisesresistive means, the resistance of whiCh varies logarithmically with theambient parameter.
 9. The transducer of claim 8 wherein said resistivemeans is biased with A. C. power and said oscillator means is biasedwith D. C. power and means are provided for isolating the A. C. power ofsaid resistive means and the D.C. power of said oscillator means. 10.The transducer of claim 5 wherein said ambient paramter sensed isrelative humidity.
 11. A transducer for varying the frequency of anoscillator as a linear function of an ambient parameter comprising: a.means for sensing said ambient parameter and generating a signal whichvaries logarithmically with said ambient parameter; b. oscillator meanscoupled to said sensing means and to circuit means for generating asignal which varies exponentially with respect to time; c. means forcontrolling the frequency of said oscillator means as a combinedfunction of said logarithmic and exponential signals to thereby varysaid frequency linearly with said ambient parameter.
 12. The transducerof claim 11 wherein said ambient parameter sensed is relative humidity.13. The transducer of claim 11 wherein there is further providedbistable multivibrator means for driving a synchronous motor, saidbistable multivibrator being coupled to said oscillator means to drivesaid synchronous motor in synchronism with the frequency of saidoscillator means.
 14. The transducer of claim 11 wherein there isfurther provided semiconductor switch means for gating the output ofsaid oscillator means to said bistable multivibrator.
 15. A transducerfor varying the frequency of an oscillator as a function of an ambientparameter comprising: a. oscillator means including a semiconductormeans having a gate electrode, an anode, and a cathode, saidsemiconductor means being rendered conductive to generate output pulsesat said cathode at a frequency determined by the relative voltages atsaid gate electrode and said anode; b. means for supplying a voltage tosaid anode which varies exponentially with time; and c. means coupled tothe gate electrode of said oscillator for sensing said ambient parameterand generating a voltage at said gate which varies as a function of saidambient parameter; whereby the combined functions of the voltagesapplied to said gate and anode of said oscillator means constrain thefrequency of said oscillator means to vary as a function said ambientparameter.
 16. The transducer of claim 15 wherein said semiconductormeans is a programable unijunction transistor.
 17. The transducer ofclaim 15 wherein semiconductor gate means are provided for coupling saidoscillator means to said bistable multivibrator.
 18. The transducer ofclaim 15 wherein said means for sensing said ambient parameter comprisesresistive means, the resistance of which varies logarithmically with theambient parameter.
 19. The transducer of claim 18 wherein said resistivemeans is biased with the A. C. power and said oscillator means is biasedwith D. C. power and means are provided for isolating the A. C. power ofsaid resistive means and the D. C. power of said oscillator means. 20.The transducer of claim 15 wherein said ambient parameter sensed isrelative humidity.
 21. The transducer of claim 5 wherein the voltage atthe gate of said semiconductor means varies exponentially with saidambient parameter and the frequency of said oscillator means varieslinearly with said ambient parameter.
 22. The transducer of claim 15wherein the voltage at the gate of said semiconductor means variesexponentially with said ambient parameter and the frequency of saidoscillator means varies linearly with said ambient parameter.
 23. Atranducer for driving a motor at speeds which vary as a linear functionof an ambient parameter comprising: a. means for sensing said ambientparameter and generating a first signal which varies as a firstnonlinear function with changes in said ambient parameter; b. oscillAtormeans for producing an oscillating signal; c. circuit means coupled tosaid oscillator for producing a second signal which varies as a secondand different nonlinear function with respect to time; d. means couplingsaid sensing means to said oscillator means for changing said secondsignal to a third nonlinear signal; e. said second and third signalscontrolling said oscillator to vary the oscillator frequency as a linearfunction of change in said ambient parameter; f. a synchronous motor;and g. means for coupling said oscillator signal to said motor forcontrolling the speed of said motor as a linear function of change insaid ambient parameter.